Well, i've read some articles and reviewed some benchmarks and the overall performance gain from the X-FI in gaming isn't greatly increased. Both X-FI & Audigy 2 ZS benches were nearly identical. This is also due to the fact that games haven't been designed to utilize the X-FI's capabilities. Much the same as the dual cores at this point.
The only increase in audiable performance was Battlefield 2. Which when designed included a X-FI setting in the audio settings. It's been reported that many more sounds are heard during all parts of gameplay and more distinct sounds in full surround. Like it's easy to tell that your player is walking through graval, sticks and leaves, because you can easily hear all three. And also, you'd be able to hear those sounds of footsteps while firing your weapon or having artillery dropped near you...
But... we'll see once a few months goes by how these new cards really are...